Saturday, August 31, 2013

Into the Great Unknown: Exploring the Heart of a Long-Gone Mountain Range (and words from home!)

We were really out of touch. In the eight days we had been gone on the Colorado River (the Great Unknown), I sent one text from camp the first night (surprise, cellular coverage at mile 6!), and on the second or third night I had a two-minute conversation on the emergency satellite phone (we couldn't download a waiting message on the phone so we each checked on our loved ones; it turned out to be a "Welcome to Verizon" message or whatever satellite company it was). I had seen not a single sign of any sort since we left Lee's Ferry aside from some number markers on the Unkar Ruins trail. So the beginning of our day was a real culture shock. Less than a quarter mile from our camp at Cremation, a bridge came into view!

And what a bridge! For something like 400 miles, from Lee's Ferry to Pat Tilman Bridge and Hoover Dam not a single bridge crosses the Colorado River. How many rivers in the world in this day and age have that kind of a record? In any case, it was not a bridge for cars, but for hikers and mule trains. We had reached Grand Central Station of the Grand Canyon: Phantom Ranch.

Just how urbanized is Phantom Ranch? It has signs for one, like this one that greets boaters fresh off the river. And there are water spigots with treated water just 100 yards from the boat beach (our fresh water stores were becoming slim). And there were two dozen or more things called permanent "buildings", which apparently are used by other human beings for cooking, sleeping, showering, and even eliminating human waste! With flushing water! One of the most amazing contraptions I saw was a "pay telephone", an instrument I was able to use to contact the outside world for news. I was relieved to find that there had been no zombie apocalypse, and that life was more or less normal beyond the rim of the canyon.

And...there is green stuff all over the place, in spite of the 100+ degree temperatures that last all through the summer season. Cottonwood trees and grass and stuff. It turns out that Phantom Ranch was located along Bright Angel Creek, one of the larger tributary streams flowing into the Grand Canyon. Bright Angel Creek begins in earnest at Roaring Springs around 10 miles upstream. The water bursts out of the rock at the base of the Muav Limestone as an instant river. There is so much water that pumping stations were built so that the springs supply the water needs of the developments at both the North Rim and South Rim of Grand Canyon National Park: all the hotels, the campgrounds, the visitor centers, and the restrooms. And there is enough left over that the creek flows all year at the Ranch and supports a robust population of fish (eight native species originally and two introduced trout species that are being removed).

After talking on the phone, mailing postcards, and consuming both the most expensive and most refreshing iced lemonade I've ever had, we got back on the rafts and began the second half of our journey. A short distance downstream, just below the second footbridge, we met the new members of our party, and had lunch (salmon salad pitas).

We were deep within the Granite Gorge and not a whole lot of granite was to be seen. The cliffs were mostly composed of dark schist or gneiss. There were thin dikes and stringers of red and pink granite and pegmatite here and there. But still, looking at the sheer walls coming straight down to the water, I could understand the apprehension of John Wesley Powell and his men as they ventured through this canyon in 1869. They were getting used to rapids by this point, but they had almost always been able to portage the boats around the worst rapids, or let them down the raging river by rope. Both of these methods were difficult at best, but with the sheer walls they were forced to run some rapids that they would have rather avoided.

We were approaching our first class 9 rapid at Horn Creek. As we went in, I experienced one of the really big holes with a huge standing wave. We kind of shot right through it, meaning I was thoroughly and completely drenched.

It took awhile to dry off enough that I felt I could retrieve my camera from the dry bag, so my picture looking back at Horn Creek Rapid makes it look a great deal smaller than it actually is (below).

Perhaps the comic I drew that night can provide some perspective...

We moved on downstream. It was a short day on the river, only five miles total, so we drifted with the current for awhile, passing gigantic towers of schist and granite. The peak in the picture below reminded me of Sentinel Rock in Yosemite Valley.

We passed an intriguing little island just before camp, with a tamarisk tree surviving somehow on a solid mass of schist and granite. This rock and the tree must surely be inundated during high water, and soil must be washed away on a continual basis. Then again, as of 1963 the flows of the river have been tightly controlled, with only a few floods (planned and unplanned) since then.

With the leisurely day, I had a chance to take some close up shots of the metamorphic rocks.

The forms are fascinating. As we noted in yesterday's post, these rocks are the deep crust remnants of a 1.7 billion year old mountain range that once extended from at least California (Death Valley area) to Mexico and perhaps Oklahoma and Arkansas. The mountains were pushed up as a result of the collisions between a series of island terranes and the core of the North American continent.

These rocks used to be mud and silt on the ocean floor, or volcanic rock like one sees in Japan or the Aleutian Islands. The rocks were crushed, buried, and heated nearly to the melting point, but not quite (different minerals melt at different temperatures, so part of the rock could have been molten, but not all of it). The rocks were twisted and folded like saltwater taffy, and later on they were intruded by hot masses of granitic magma, forming the pink rock in these pictures.

The granite has huge crystals of potassium feldspar (the pink/orange mineral), clear quartz, and plates or sheets of shiny muscovite mica. Such rocks are called pegmatites. Other beautiful minerals can sometimes be seen, including black biotite mica, and reddish brown garnet.

I was walking in a small unnamed canyon just upstream of Salt Creek (our camp was very creatively called "Above Salt Creek"). There was a small trickle of water.

The little bit of erosion has attacked the boundary between the schist and the granite, highlighting a fold in the schist.

My ankles were bothering me again, so there was no way I was going try to climb the jumble of boulders at the head of the canyon, but before I got there my attention was drawn to one of the strangest rocks I had seen in awhile. It was bright red.

Most of the time, geologists are pretty loose with their definition of the color red, using it to describe a lot of brown and reddish brown rocks and sediments. But this stuff was really red. It was essentially fine-grained, but may have had small phenocrysts (small crystals) of a white mineral, maybe feldspar. I couldn't tell, and to my shame I was caught in the wild without my handlens! It was fairly easy to weather, as you can see from the mineral veins that stand out in relief (this is material, probably calcium carbonate, that filled cracks and fissures in the rock much later).

I'm guessing it might have been some kind of metavolcanic rock, but really as a non-petrologist, I am not at all sure. Any ideas out there, gang?

The shadows grew longer in the dark canyon as the boatmen checked their rigs. Tomorrow was promising to be the most challenging day of the trip, with at least ten major rapids, including Granite (8), Hermit (8), and Crystal (9-10).

We were treated to a wonderful sunset. Once again I hit the sack early, just moments after sunset.

Horn Rapids was the one that "got" us. First rapids after we switched out half of our crew (fortunately none of the oarsmen). But we had one short paddle boat that carried 6 people plus a pilot -- the first wave turned us a bit and we hit the biggest wave almost sideways, dumping a couple of people. It was a big wake-up call after a relatively uneventful 8 days, especially knowing that we had a big day coming up and Lava to look forward to...

About Me

I am a teacher of geology at Modesto Junior College and former president of the National Association of Geoscience Teachers, Far Western Section. I have led field trips all over the western United States, and a few excursions overseas, but my homebase is the Sierra Nevada, the Great Valley, and the Coast Ranges of California.